Although Internet Explorer (IE) continues to slowly lose the war for browser share, its rate of decline has slowed since Microsoft launched IE8, according to data from one Web metrics firm.

Data from another often-cited measurement company, however, shows little or any reduction in IE's drop.

In the last three years, Microsoft's browser has lost 25% of its usage share as measured by U.S.-based Net Applications, a decline that took it from a once-overwhelming share of 79.5% in November 2007 to the narrow majority of September 2010's 59.7%.

Over a shorter period -- from July 2008 to September 2010 -- Irish company StatCounter tallied an even larger fall for IE, which lost 27% of its share during the two-year-plus span.

StatCounter pegged IE's overall share last month at 49.9%, a minority milestone that many noted.

But the two Web tracking companies disagree over whether IE's decline has slowed since the launch of IE8 in March 2009.

In the 17 months prior to IE8's appearance, Net Applications tracked an IE tumble of 11.7 percentage points, a decline of 15%. But in the 17 months after IE8's debut, Microsoft's total browser share dropped by significantly less in absolute numbers -- only 8.1 points -- as well as in a percentage of share, with the post-IE8 decline representing 12% of IE's share at the start of the period.

StatCounter's statistics, meanwhile, do not go back as far as Net Applications' and show little if any slowdown in IE's slide.

In the eight months before IE8's launch, Microsoft's numbers fell by 6.7 points, a 9.8% share loss. During the eight months after IE8's March 2009 unveiling, Microsoft's share declined by slightly less in absolute numbers -- 6.6 percentage points -- but fell lightly more as a percentage of share, posting a 10.7% drop from the beginning to the end of the period.

IE8's impact is important to Microsoft, which pitched the 2009 program as its return to the "modern" browser race. The company's hope to keep IE relevant in the face of frequently-updated rivals such as Mozilla's Firefox and Google's Chrome is largely pinned on IE8, which is the browser bundled with Windows 7, the operating system Microsoft has touted as its most successful ever.

If IE8 is unable to stem Microsoft's slide in usage share, there's little chance of its next browser, IE9, doing the same, if only because the new version will not run on Windows XP, the Microsoft operating system that still powers about two out of every three Windows PCs.

IE9 is currently in beta testing, but won't ship in final form until 2011.

The primary beneficiary of IE's decline, IE8 notwithstanding, has been Google's Chrome, which has gained 6.2 of its 8 total percentage points since March 2009, according to Net Applications.

StatCounter, which did not start tracking Chrome until July 2009, had Chrome's share at a more substantial 11.4% as of September 2010, putting all of that increase in the post-IE8 period.

By the numbers from both Net Applications and StatCounter, Mozilla's Firefox and Apple's Safari have lost share or gained less ground than Chrome, respectively, since IE8's introduction.